Carbon fiber is known to be produced from polyethylene fiber by first stabilizing the precursor fiber by liquid immersion sulfonation (e.g., by treatment with chlorosulfonic or sulfuric acid) to make an infusible precursor, and the infusible precursor subjected to pyrolysis to make the carbon fiber. Without the stabilization process, the polyethylene fiber would not be thermally infusible, and therefore, not carbonizable at the high temperatures employed for carbonization.
Rapid stabilization via sulfonation of polyethylene precursor fibers is desired for favorable process economics. However, a key problem encountered in the rapid-stabilization process is that the resulting carbon fiber often lacks sufficient strength and other mechanical properties (more specifically, adequate tensile strength and elastic modulus) for applications in which such robust characteristics are needed. Thus, there would be a clear and present advantage in an improved stabilization method that results in higher strength and more robust carbon fibers.
Polymeric fibers with high degree of molecular orientation have high tensile strength and modulus. Sulfonation of polyethylene causes shrinkage in the fiber, with more rapid sulfonation causing a higher degree of fiber shrinkage. The shrinkage force due to sulfonation is substantial for highly oriented fibers, and high orientation imparts more tolerance to shrinkage force. Therefore, a combination of all these would be necessary to attain a preferred fiber morphology via a directed alteration of process sequence that leads to precursor and precursor-derived carbon with long-range order.